2.1 Exercise-Induced Asthma
Asthma is a pulmonary disease characterized by reversible airway obstruction, airway inflammation, and increased airway responsiveness to a variety of stimuli. The Merck Manual, 556-568 (17th ed., 1999).
Exercise-induced asthma (EIA) is a condition of respiratory difficulty that is triggered by aerobic exercise lasting several minutes. McFadden et al., Exercise-induced asthma, N Engl J Med, 1994 May 12; 330(19): 1362. Patients usually complain of exercise-related respiratory symptoms. This complaint is much more common among children and younger athletes but can be seen at any age. Symptoms during or following exercise include chest tightness, chest pain, cough, shortness of breath, wheezing, stomach ache and fatigue. Hough et al., Exercise-induced asthma and anaphylaxis, Sports Med, 1994 September; 18(3): 164; and Storms, Asthma associated with exercise, Immunol Allergy Clin North Am, 2005 February; 25(1): 37.
EIA affects 12-15% of the population in the United States of America. EIA is experienced by 90% of asthmatic individuals and 35-45% of people with allergic rhinitis. Even when eliminating those with rhinitis and allergic asthma, a 3-10% incidence of EIA is seen in the general population. EIA seems to be more prevalent in some winter or cold-weather sports. Some studies have demonstrated rates as high as 35% or even 50% in competitive-caliber figure skaters, ice hockey players, and cross-country skiers. Hough et al., page 163; and Lacroix, Exercise-induced asthma, Phys Sports Med, 1999; 27: 75.
Although the exact mechanism is unknown, there are two predominant theories as to how the symptom of EIA is triggered. Storms, page 32. One is hyperosmolarity theory or airway humidity theory, which suggests that air movement through the airway results in relative drying of the airway. Id. This in turn is believed to trigger a cascade of events that results in airway edema, secondary to hyperemia and increased perfusions in an attempt to combat the drying. This is believed to lead to the release of mediators that cause bronchoconstriction. The mediators include histamine, prostaglandin, and leukotriene. Id.
The other theory is airway rewarming theory. It is based on airway cooling and assumes that the air movement in the bronchial tree results in a decreased temperature of the bronchi, which may also trigger a hyperemic response in an effort to heat the airway. This leads to congested vessels, fluid exudation from the blood vessels into the submucosa of the airway wall, and mediator release with subsequent bronchoconstriction. Id.
Causes of EIA can be divided into the categories of medical, environmental, and drug-related. Lacroix, pages 75-92. Poorly controlled asthma or allergic rhinitis results in increased symptoms with exercise. Secretions of hay fever can aggravate EIA. Viral, bacterial, and other forms of upper respiratory infections also aggravate the symptoms of EIA. Excess of pollens or molds in the air can exacerbate EIA. Id. Pollutants such as cigarette smoke, sulfur dioxide and nitrogen oxide in the air are irritants to the airways and can lower the threshold for symptomatic bronchospasm. Id. Chemicals used in certain sports for environmental maintenance can worsen EIA symptoms. Aspirin and beta-blockers are also known as asthmatogenic agents. Id.
Still, there is a significant need for safe and effective methods of treating, preventing and managing exercise induced asthma, particularly for patients that are refractory to conventional treatments, while reducing or avoiding the toxicity and/or side effects associated with conventional therapies.